class Metamodel::ClassHOW
    does Metamodel::Naming
    does Metamodel::Documenting
    does Metamodel::Versioning
    does Metamodel::Stashing
    does Metamodel::AttributeContainer
    does Metamodel::MethodContainer
    does Metamodel::PrivateMethodContainer
    does Metamodel::MultiMethodContainer
    does Metamodel::RoleContainer
    does Metamodel::MultipleInheritance
    does Metamodel::DefaultParent
    does Metamodel::C3MRO
    does Metamodel::MROBasedMethodDispatch
    does Metamodel::MROBasedTypeChecking
    does Metamodel::Trusting
    does Metamodel::BUILDPLAN
    does Metamodel::Mixins
    does Metamodel::ArrayType
    does Metamodel::BoolificationProtocol
    does Metamodel::REPRComposeProtocol
    does Metamodel::InvocationProtocol
    does Metamodel::Finalization
        { }

Warning: this class is part of the Rakudo implementation, and is not a part of the language specification.

Metamodel::ClassHOW is the metaclass behind the class keyword.

say so Int.HOW ~~ Metamodel::ClassHOW;    # OUTPUT: «True␤» 
say Int.^methods(:all).pick.name;         # OUTPUT: «random Int method name␤»

Methods

method add_fallback

method add_fallback($obj, $condition, $calculator)

Installs a method fallback, that is, add a way to call methods that weren't statically added.

Both $condition and $calculator must be callables that receive the invocant and the method name once a method is called that can't be found in the method cache.

If $condition returns a true value, $calculator is called with the same arguments, and must return the code object to be invoked as the method, and is added to the method cache.

If $condition returns a false value, the next fallback (if any) is tried, and if none matches, an exception of type X::Method::NotFound is thrown.

User-facing code (that is, code not dabbling with metaclasses) should use method FALLBACK instead.

method can

method can($obj, $method-name)

Given a method name, it returns a List of methods that are available with this name.

class A      { method x($a) {} };
class B is A { method x()   {} };
say B.^can('x').elems;              # OUTPUT: «2␤» 
for B.^can('x') {
    say .arity;                     # OUTPUT: «1, 2␤» 
}

In this example, class B has two possible methods available with name x (though a normal method call would only invoke the one installed in B directly). The one in B has arity 1 (i.e. it expects one argument, the invocant (self)), and the one in A expects 2 arguments (self and $a).

method lookup

method lookup($obj, $method-name --> Method:D)

Returns the first matching Method with the provided name. If no method was found, returns a VM-specific sentinel value (typically a low-level NULL value) that can be tested for with a test for definedness. It is potentially faster than .^can but does not provide a full list of all candidates.

    say Str.^lookup('Int').raku; # OUTPUT: «method Int (Str:D $: *%_) { #`(Method|39910024) ... }␤» 
 
    for <upper-case  uc> {
        Str.^lookup: $^meth andthen .("foo").say
            orelse "method `$meth` not found".say
    }
    # OUTPUT: 
    # method `upper-case` not found 
    # FOO 

method compose

method compose($obj)

A call to compose brings the metaobject and thus the class it represents into a fully functional state, so if you construct or modify a class, you must call the compose method before working with the class.

It updates the method cache, checks that all methods that are required by roles are implemented, does the actual role composition work, and sets up the class to work well with language interoperability.

method new_type

method (:$name, :$repr = 'P6opaque', :$ver, :$auth)

Creates a new type from the metamodel, which we can proceed to build

my $type = Metamodel::ClassHOW.new_type(name => "NewType",
                                        ver => v0.0.1,
                                        auth => 'github:perl6' );
$type.HOW.add_method($type,"hey", method { say "Hey" });
$type.hey;     # OUTPUT: «Hey␤» 
$type.HOW.compose($type);
my $instance = $type.new;
$instance.hey; # OUTPUT: «Hey␤»

We add a single method by using Higher Order Workings methods, and then we can use that method directly as class method; we can then compose the type, following which we can create already an instance, which will behave in the exact same way.